feat(ui): Repeat xd-client UI with modern adaptive features

- Integrated Tailwind CSS v4 and Shadcn UI components from xd-client
- Adopted xd-client modern aesthetic (oklch, radial gradients, glassmorphism)
- Combined with modern adaptive 3-tier navigation logic
- Refactored all pages (Profile, Login, Settings, Messages, Schedule, Grades, Debts)
- Enhanced ThemeProvider with dynamic Material You palette generation
- Polished overall UX and animations

Refs #3
Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/utils.ts

@@ -0,0 +1,6 @@
+import { type ClassValue, clsx } from "clsx";
+import { twMerge } from "tailwind-merge";
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}